The modeling, design, simulation, fabrication, calibration, and testing of a three-element, 15.3 cm fiber Bragg grating strain sensor array with the coherent optical frequency domain reflectometry (C-OFDR) interrogation technique are demonstrated. The fiber Bragg grating array (FBGA) is initially simulated using in-house software that incorporates transfer matrices. Compared to the previous techniques used, the transfer matrix method allows a systemwide approach to modeling the FBGA-C-OFDR system. Once designed and simulated, the FBGA system design is then imprinted into the core of a boron-germanium codoped photosensitive fiber using the phase mask technique. A fiber optic Fabry-Perot interferometric (FPI) strain gauge calibrator is then used to determine the strain gauge factor of a single fiber Bragg grating (FBG), and the results are used on the FBGA. The FPI strain gauge calibrator offers nondestructive testing of the FBG. To test the system, the FBGA is then attached to a 75 cm cantilever beam and interrogated using an incremental tunable laser. Electric strain gauges (ESGs) are then used to independently verify the strain measurements with the FBGA at various displacements of the cantilever beam. The results show that the peak strain error is 18% with respect to ESG results. In addition, good agreement is shown between the simulation and the experimental results.
Detection and characterization of chemical contaminants in water network is paramount for water quality and water security. The current trend of monitoring the presence of contaminants is the batch sampling technique, where sample of water is collected and analyzed in the laboratory. While this technique is accurate, it fails to provide immediate information. In this work, the authors investigate the effectiveness of utilizing a fiber optics based sensor for detecting ammonia in water. In order for the system to sense ammonia, a small portion of the cladding of the fiber optic cable is stripped and replaced by a porous polymer material. A novel procedure of etching the glass cladding is reported. The modified cladding when interacts with ammonia causes a change in intensity of the electromagnetic wave flowing through the cable. The change in intensity caused by the modified cladding is studied parametrically which will help in forming a correlation between concentration of ammonia and absorbance.
Pattern discovery algorithms based on the computational mechanics (CM) method have been shown to succinctly describe underlying patterns in data through the reconstruction of minimum probabilistic finite state automata (PFSA). We apply the CM approach toward the tracking of human subjects in real time by matching and tracking the underlying color pattern as observed from a fixed camera. Objects are extracted from a video sequence, and then raster scanned, decomposed with a one-dimensional Haar wavelet transform, and symbolized with the aid of a red-green-blue (RGB) color cube. The clustered causal state algorithm is then used to reconstruct the corresponding PFSA. Tracking is accomplished by generating the minimum PFSA for each subsequent frame, followed by matching the PFSAs to the previous frame. Results show that there is an optimum alphabet size and segmentation of the RGB color cube for efficient tracking.
A theoretical method for the suppression of cavity interference is described that suppresses the cavity interference in a fiber Bragg grating array (FBGA) interrogated using the coherent optical frequency domain reflectometry (C-OFDR) technique. In C-OFDR, a tunable laser source is used to scan an interferometer, composed of a FBGA and a broadband reference reflector, as a function of wavelength. The interference between the FBGA and the reference reflector results in a composite modulated interferometric signal. A Fourier transform of this signal is then made to spatially separate out each fiber Bragg grating (FBG) in the array. In this work, the undesirable cavity interference component of this signal is simultaneously suppressed by directly subtracting the cavity interference signal from the overall interference signal. This method is simulated with polarization optics and a circularly polarized tunable laser source. The cavity suppression method allows the C-OFDR/FBGA to operate at half the bandwidth of the downshifting method, potentially saving optical fiber material, and at a higher return signal than the FBG reflectance reduction method. In addition, the detection system is polarization insensitive.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.